CMOS (Complementary Metal-Oxide Semiconductor): The semiconductor technology used in the transistors that are manufactured into most of today's computer microchips.
BIOS (Basic Input Output System): The program a personal computer's microprocessor uses to get the computer system started after you turn it on. It also manages data flow between the computer's operating system and attached devices such as the hard disk, video adapter, keyboard, mouse, and printer.
EEPROM (Electronically Erasable Programmable Read-Only Memory): a computer chip that can be erased by exposing it to an electrical charge.
POST (Power On Self Test): Diagnostic testing sequence that a computer's BIOS runs to determine if the computer keyboard, random access memory, disk drives, and other hardware are working correctly.
When a computer is first powered on, the BIOS is the first thing executed by the system. The BIOS provides a basic set of instructions used to boot the computer.
The BIOS performs all the tasks which need to be done at startup including performing self diagnostics and initializing the hardware in the computer (also known as the POST process).
On most current motherboards, the BIOS is stored in an EEPROM, also known as a "Flash" BIOS, to allow users to upgrade the BIOS if updates are made available.
The BIOS provides a setup program (commonly called the CMOS Setup) which allows the user to adjust a variety of settings related to the BIOS operation and hardware setup such as CPU Clock speed, memory timing, time and date functions, disk configuration, etc.
These "BIOS configuration" settings are stored in a chip known as CMOS and loaded by the BIOS as the system starts.
In general, the BIOS configuration of the computer should be left at its "default" settings. Changes to the BIOS should only be made if specifically noted in the documentation for your motherboard or any additional hardware you might install into the PC.
An incorrect BIOS configuration can negatively impact the performance and functionality of the system.
An incorrect BIOS configuration can cause various issues such as:
When a computer is first powered on, the system will begin to POST. During this process, most motherboards will display a "BIOS string".
The BIOS string can provide information about the motherboard manufacturer and motherboard model along with details on the BIOS revision and release date. Details on decoding BIOS string for a given motherboard can generally be obtained by visiting the website for your motherboard manufacturer.
During POST, the BIOS will perform some basic system hardware diagnostics. If a hardware problem is found during post, the BIOS may provide a beep code or numeric code to indicate the type of problem found.
Most BIOS manufacturers provide information on identifying the meaning of the error codes along with other helpful information and utilities on their websites:
Motherboard and BIOS manufacturers will often offer BIOS updates for specific motherboards.
These BIOS updates can:
If you are experiencing a hardware related problem, you may wish to consider updating your motherboard's BIOS. To determine whether a BIOS update is available for your system, please contact the system or motherboard's manufacturer.
As previously noted, in most instances, you will want to leave the BIOS settings for your system at their "default" settings.
If the BIOS settings have been changed for any reason, re-setting the BIOS to its predefined defaults can help to troubleshoot issues such as system lockups, posting errors, performance issues, display corruption, and other low level hardware related problems. Prior to setting the BIOS to its defaults, be sure to document the current settings for the various BIOS options so that you will be able to restore them if required.
Most motherboards are shipped with factory default BIOS settings that are optimized for stability and compatibility. The factory default configuration can be modified to allow for the use of higher performance settings.
Many BIOSes will also offer an option for "Performance settings". Performance settings, while often improving the speed at which the system will run, can compromise system stability. Therefore, you should consider disabling any performance options if you are experiencing system problems.
The BIOS usually beeps once at the end of POST to prove the speaker is working correctly (some manufacturers may modify or disable this feature). However, if an error is detected, the BIOS program will:
1. Display the error to the screen if possible.
2. Generate a POST beep code using the computer's internal speaker if it cannot access the display adaptor.
AMI (American Megatrends International) Beep Codes
|Beep Code||Description / What to Check|
|1 beep||DRAM refresh failure. There is a problem in the system memory
or the motherboard.
|2 beeps||Memory parity error. The parity circuit is not working properly.|
|3 beeps||Base 64K RAM failure. There is a problem with the first 64K
of system memory.
|4 beeps||System timer not operational. There is problem with the timer(s)
that control functions on the motherboard.
|5 beeps||Processor failure. The system CPU has failed.|
|6 beeps||Gate A20/keyboard controller failure. The keyboard IC controller
has failed, preventing gate A20 from switching the processor to protect
|7 beeps||Virtual mode exception error.|
|8 beeps||Video memory error. The BIOS cannot write to the frame buffer
memory on the video card.
|9 beeps||ROM checksum error. The BIOS ROM chip on the motherboard is
|10 beeps||CMOS checksum error. Something on the motherboard is causing
an error when trying to interact with the CMOS.
|11 beeps||Bad cache memory. An error in the level 2 cache memory.|
|1 long beep, 2 short||Failure in the video system.|
|1 long beep, 3 short||A failure has been detected in memory above 64K.|
|1 long beep, 8 short||Display test failure.|
|Continuous beeping||A problem with the memory or video.|
Award BIOS beep codes
Award uses the least of any of the BIOS manufactures just two codes, they prefer to display a message on the screen state the error. The only time you will get any beeps during POST is if there is a problem with the video card, CPU or memory. While the computer is running a high pitched repeating beep may indicate the CPU is overheating.
|Beep Code||Description / What to Check|
|1 Long, 2 or 3 Short||A video error has occurred and the Bios cannot initialise
the video screen to display any additional information.
|Repeating High, Low beeps||CPU failure|
|Repeating beep(s)||RAM Problem.|
Phoenix BIOS beep codes
Phoenix beep codes are the most detailed about. Instead of using short and long beeps Phoenix use a system of 4 beeps which are separated by a small pause.(
beep pause beep, beep pause beep pause beep pause beep, beep = 1-2-1-2)
|Beep Code||Description / What to Check|
|1-1-1-3||Verify Real Mode.|
|1-1-2-1||Get CPU type.|
|1-1-2-3||Initialize system hardware.|
|1-1-3-1||Initialize chipset registers with initial POST values.|
|1-1-3-2||Set in POST flag.|
|1-1-3-3||Initialize CPU registers.|
|1-1-4-1||Initialize cache to initial POST values.|
|1-2-1-1||Initialize Power Management.|
|1-2-1-2||Load alternate registers with initial POST values.|
|1-2-1-3||Jump to UserPatch0.|
|1-2-2-1||Initialize keyboard controller.|
|1-2-2-3||BIOS ROM checksum.|
|1-2-3-1||8254 timer initialization.|
|1-2-3-3||8237 DMA controller initialization.|
|1-2-4-1||Reset Programmable Interrupt Controller.|
|1-3-1-1||Test DRAM refresh.|
|1-3-1-3||Test 8742 Keyboard Controller.|
|1-3-2-1||Set ES segment to register to 4 GB.|
|1-3-3-1||28 Autosize DRAM.|
|1-3-3-3||Clear 512K base RAM.|
|1-3-4-1||Test 512 base address lines.|
|1-3-4-3||Test 512K base memory.|
|1-4-1-3||Test CPU bus-clock frequency.|
|1-4-2-4||Reinitialize the chipset.|
|1-4-3-1||Shadow system BIOS ROM.|
|1-4-3-2||Reinitialize the cache.|
|1-4-4-1||Configure advanced chipset registers.|
|1-4-4-2||Load alternate registers with CMOS values.|
|2-1-1-1||Set Initial CPU speed.|
|2-1-1-3||Initialize interrupt vectors.|
|2-1-2-1||Initialize BIOS interrupts.|
|2-1-2-3||Check ROM copyright notice.|
|2-1-2-4||Initialize manager for PCI Options ROMs.|
|2-1-3-1||Check video configuration against CMOS.|
|2-1-3-2||Initialize PCI bus and devices.|
|2-1-3-3||Initialize all video adapters in system.|
|2-1-4-1||Shadow video BIOS ROM.|
|2-1-4-3||Display copyright notice.|
|2-2-1-1||Display CPU type and speed.|
|2-2-2-1||Set key click if enabled.|
|2-2-2-3||56 Enable keyboard.|
|2-2-3-1||Test for unexpected interrupts.|
|2-2-3-3||Display prompt "Press F2 to enter SETUP".|
|2-2-4-1||Test RAM between 512 and 640k.|
|2-3-1-1||Test expanded memory.|
|2-3-1-3||Test extended memory address lines.|
|2-3-2-1||Jump to UserPatch1.|
|2-3-2-3||Configure advanced cache registers.|
|2-3-3-1||Enable external and CPU caches.|
|2-3-3-3||Display external cache size.|
|2-3-4-1||Display shadow message.|
|2-3-4-3||Display non-disposable segments.|
|2-4-1-1||Display error messages.|
|2-4-1-3||Check for configuration errors.|
|2-4-2-1||Test real-time clock.|
|2-4-2-3||Check for keyboard errors|
|2-4-4-1||Set up hardware interrupts vectors.|
|2-4-4-3||Test coprocessor if present.|
|3-1-1-1||Disable onboard I/O ports.|
|3-1-1-3||Detect and install external RS232 ports.|
|3-1-2-1||Detect and install external parallel ports.|
|3-1-2-3||Re-initialize onboard I/O ports.|
|3-1-3-1||Initialize BIOS Data Area.|
|3-1-3-3||Initialize Extended BIOS Data Area.|
|3-1-4-1||Initialize floppy controller.|
|3-2-1-1||Initialize hard-disk controller.|
|3-2-1-2||Initialize local-bus hard-disk controller.|
|3-2-1-3||Jump to UserPatch2.|
|3-2-2-1||Disable A20 address line.|
|3-2-2-3||Clear huge ES segment register.|
|3-2-3-1||Search for option ROMs.|
|3-2-3-3||Shadow option ROMs.|
|3-2-4-1||Set up Power Management.|
|3-2-4-3||Enable hardware interrupts.|
|3-3-1-1||Set time of day.|
|3-3-1-3||Check key lock.|
|3-3-3-1||Erase F2 prompt.|
|3-3-3-3||Scan for F2 key stroke.|
|3-3-4-3||Clear in-POST flag.|
|3-4-1-1||Check for errors|
|3-4-1-3||POST done--prepare to boot operating system.|
|3-4-2-3||Check password (optional).|
|3-4-3-1||Clear global descriptor table.|
|3-4-4-1||Clear parity checkers.|
|3-4-4-3||Clear screen (optional).|
|3-4-4-4||Check virus and backup reminders.|
|4-1-1-1||Try to boot with INT 19.|
|4-2-1-1||Interrupt handler error.|
|4-2-1-3||Unknown interrupt error.|
|4-2-2-1||Pending interrupt error.|
|4-2-2-3||Initialize option ROM error.|
|4-2-3-3||Extended Block Move.|
|4-2-4-1||Shutdown 10 error.|
|4-3-1-3||Initialize the chipset.|
|4-3-1-4||Initialize refresh counter.|
|4-3-2-1||Check for Forced Flash.|
|4-3-2-2||Check HW status of ROM.|
|4-3-2-3||BIOS ROM is OK.|
|4-3-2-4||Do a complete RAM test.|
|4-3-3-1||Do OEM initialization.|
|4-3-3-2||Initialize interrupt controller.|
|4-3-3-3||Read in bootstrap code.|
|4-3-3-4||Initialize all vectors.|
|4-3-4-1||Boot the Flash program.|
|4-3-4-2||Initialize the boot device.|
|4-3-4-3||Boot code was read OK.|